Common Sense Media says that VidRhythm (free for iPhone and iPad) is "one of the oddest music games" parents are likely to see. It certainly targets different skills than just simple music appreciation and instrument recognition!
This music app for tweens and teens allows kids to input their own voices, videos, and images and use those samples with VidRhythm's music library to create mashup videos. Or, if you have MIDI capability, your child can upload their own music to use.
However they choose to use it, be prepared to hear a lot of autotune and see some crazy video production at work!